Androgens are the anabolic steroid hormones of animals, controlling muscle and skeletal mass, the maturation of the reproductive system, the development of secondary sexual characteristics and the maintenance of fertility in the male. In women, testosterone is converted to estrogen in most target tissues, but androgens themselves may play a role in normal female physiology, for example, in the brain. The chief androgen found in serum is testosterone, and this is the effective compound in tissues such as the testes and pituitary. In prostate and skin, testosterone is converted to 5α-dihydrotestosterone (DHT) by the action of 5α-reductase. DHT is a more potent androgen than testosterone because it binds more strongly to the androgen receptor.
Like all steroid hormones, androgens bind to a specific receptor inside the cells of target tissues, in this case the androgen receptor. This is a member of the nuclear receptor transcription factor family. Binding of androgen to the receptor activates it and causes it to bind to DNA binding sites adjacent to target genes. From there it interacts with coactivator proteins and basic transcription factors to regulate the expression of the gene. Thus, via its receptor, androgens cause changes in gene expression in cells. These changes ultimately have consequences on the metabolic output, differentiation or proliferation of the cell that are visible in the physiology of the target tissue.
Although modulators of androgen receptor function have been employed clinically for some time, both the steroidal (Basaria, S., Wahlstrom, J. T., Dobs, A. S., J. Clin Endocrinol Metab (2001), 86, pp 5108-5117; Shahidi, N. T., Clin Therapeutics, (2001), 23, pp 1355-1390), and non-steroidal (Newling, D. W., Br. J. Urol., 1996, 77 (6), pp 776-784) compounds have significant liabilities related to their pharmacological parameters, including gynecomastia, breast tenderness and hepatotoxicity. In addition, drug-drug interactions have been observed in patients receiving anticoagulation therapy using coumarins. Finally, patients with aniline sensitivities could be compromised by the metabolites of non-steroidal antiandrogens.
Non-steroidal agonists and antagonists of the androgen receptor are useful in the treatment of a variety of disorders and diseases. More particularly, antagonists of the androgen receptor could be employed in the treatment of prostate cancer, benign prostatic hyperplasia, hirsutism in women, alopecia, anorexia nervosa, breast cancer and acne. Agonists of the androgen receptor could be employed in male contraception, male performance enhancement, as well as in the treatment of cancer, AIDS, cachexia, and other disorders. Additionally, agonists of the androgen receptor are useful in promoting burn recovery (Murphy, K. D., Suchmore, T., Micak, R. P., Chinkes, D. L., Klein, G. L., Herndon, D. N., Effects of long-term oxandrolone administration in severely burned children, Surgery, (2004), 136(2), pp 219-224).
Nonetheless, there exists a need for small molecule, non-steroidal antagonists of the androgen receptor. We now describe a novel series of 2-substituted benzimidazole derivatives useful as androgen receptor modulators.